Methods of Enhanced Oil Recovery (EOR) from an oil reservoir by CO2 flooding are disclosed. One method comprises producing a well stream from the reservoir; separating the well stream into a liquid phase and a gas phase with a first gas/liquid separator, wherein the gas phase comprises both CO2 gas and hydrocarbon gas; cooling the gas phase with a first cooler; compressing the gas phase using a first compressor into a compressed stream; mixing the compressed stream with an external source of CO2 to form an injection stream; and injecting the injection stream into the reservoir. Systems for EOR from an oil reservoir by CO2 flooding are also disclosed.